1. Field of the Invention
The present invention relates to pharmaceutical dosage forms and in, particular, to a coated perforated or donut-shaped tablet for extended release of a pharmaceutically active ingredient.
2. Brief Description of the Related Art
There have been various attempts made to create extended release dosage forms for orally administering pharmaceutically active ingredients. The terms “drug” and “pharmaceutically active ingredient” are used interchangeably herein. Some dosage forms tend to release a drug at rates that do not correlate well with the needs of the patient. For example, a particular dosage form may release a large amount of a drug rapidly upon ingestion where a more constant rate of release is desirable. In other situations, varying release rates may be desirable. Additional background information on the art of controlling release rates of drugs in orally administered dosage forms is found in U.S. Pat. Nos. 5,945,125 and 6,110,500 and U.S. Published Patent Application No. US2005/0025829, the disclosures of which are incorporated herein by reference. Dosage forms typically comprise the drug; that is, the pharmaceutically active ingredient, dispersed in various excipients including polymers whose rates of dissolution are known. As the tablet is dissolved, the drug is released at a predicted rate. Coating excipients having various rates of dissolution have also been used for time delayed release of drugs.
Common oral extended release or pulsatile release dosage forms include tablets, caplets, and capsules containing small spherical pellets. Such dosage forms typically have the combined geometry of slabs and cylinders, which tend to produce varying release rates. Due to the shape, a cylindrical tablet does not follow zero order release kinetics. As the tablet is dissolved, the amount of surface area exposed to the dissolution medium changes, thereby changing the rate at which the dissolution occurs and thus the drug release rate decreases with drug release time.
When a central perforation or hole is made in an extended release tablet (donut-shaped tablet (DST)), the DST exhibits a constant drug release rate over time because a constant surface area can be radially maintained. A multi-layer DST (MLDST) can also be made as described in U.S. Published Patent Application No. US2005/0025829.
While constant drug release rates are desirable in certain circumstances, it is more generally desirable to be able to customize the kinetics of drug release. For example, a rapid initial release (a burst) may desirably be followed by a period of constant release. In other examples, it might be desirable to delay the release of the drug for a period of time or to release a pulse of the drug after a period of time delay or a period of constant release.
Hydrophilic polymers are commonly employed in extended release tablets. A problem associated with hydrophilic polymer based pharmaceutical compositions in a DST or MLDST is that these tablets can dose dump, that is, when not fully hydrated the hydrophilic polymers become very viscous and adhere to solids and biological surfaces. The surface of the tablet then peels off and the drug dosage is dumped into the patient.